topic 3 - gas exchange

Question 1

what are the two things most gas exchange surfaces have in common

Answer 1

(1) a large surface area
(2) they’re thin (often just one layer of epithelial cells) - this provides a short diffusion pathway across the gas exchange surface

Question 2

what do single celled organisms absorb and release gas

Answer 2

by diffusion through their outer surface

Question 3

why is there no need for gas exchange in single celled organisms

Answer 3

because they have a relatively large surface area, a thin surface and a short diffusion pathway (oxygen can take part in biochemical reactions as soon as it diffuses into the cell)

Question 4

what do fish use for gas exchange

Answer 4

a counter current system

Question 5

what is the first step of fish using a counter current system for gas exchange

Answer 5

water containing oxygen enters the fish through its mouth and passes out through the gills

Question 6

what are gill filaments

Answer 6

the soft, red, fleshy, thin plates that extend off the gill arch that make up the gill - through which oxygen is taken into the blood from the water passing through the gills - it increases surface area for gas exchange

Question 7

what are lamellae

Answer 7

the many tiny structures that cover gill filaments - which increases surface area even more

Question 8

what do lamellae have that speeds up diffusion

Answer 8

lots of blood capillaries and a thin surface layer of cells

Question 9

what does the lamellae have that speeds up diffusion

Answer 9

many blood capillaries and a thing surface layer of cells

Question 10

what is the counter current system in fish

Answer 10

the mechanism in which blood flows through the lamellae in one direction and water flows over in the opposite direction

Question 11

what does the counter current system maintain in fish

Answer 11

a large concentration gradient between the water and the blood - the concentration of water is always higher than in the blood, so as much oxygen as possible diffuses from the water into the blood

Question 12

what are trachea

Answer 12

microscopic air filled pipes in insects which are used for gas exchange

Question 13

what are spiracles

Answer 13

the opening in / pores on the exoskeletons of insects - found on the thorax and abdomen of insect

Question 14

what doe the trachea branch of into, what does this mean for the insect

Answer 14

smaller tracheoles which have thin, permeable walls and go to individual cells - meaning that oxygen diffuses directly into the respiring cells

Question 15

what does an insect’s circulatory system not transport

Answer 15

O2

Question 16

how is CO2 released into the atmosphere from an insect

Answer 16

CO2 from the cells move down into its own concentration gradient towards the spiracles to be released into the atmosphere

Question 17

what do insects use to move air in and out of the spiracles

Answer 17

rhythmic abdominal movements

Question 18

what is the main gas exchange surface for plants

Answer 18

the surface of the mesophyll cells in the leaf - have a large surface area

Question 19

where is the mesophyll cells found

Answer 19

inside the leaf

Question 20

what are the stomata

Answer 20

pores found on the surface of leaves, typically the ​lower epidermis - which allow for the exchange of carbon dioxide and oxygen

Question 21

where are stomata found

Answer 21

in the epidermis

Question 22

what controls the opening and closing of stomata

Answer 22

guard cells

Question 23

what does exchanging gases tend to make you lose

Answer 23

water

Question 24

what do insects do if they are loosing too much water

Answer 24

close their spiracles using muscles

Question 25

what do insects have that minimise water loss

Answer 25

a waterproof, waxy cuticle all over their body and tiny hairs around their spiracles - both of which reduce evaporation

Question 26

how does the stomata open and close in plants

Answer 26

water enters the guard cells making them turgid - causing the stomatal pore to open
if the plant becomes dehydrates, guard cells lost water and become flaccid - causing the pore to close

Question 27

what are xerophytes

Answer 27

plants especially adapted for life in warm, dry or windy habitats where water loss is a problem

Question 28

what are five examples of xerophytic adaptions

Answer 28

(1) stomata sunk in pits that trap moist air, reducing the concentration gradient of water between the leaf and the air - this reduced the amount of water diffusing out of the leaf and evaporating away
(2) a layer of hairs on the epidermis - to trap moist air round the stomata
(3) curled leaves with the stomata inside - protecting them from wind as windy conditions increase the rate of diffusion and evaporation
(4) a reduced number of stomata - so there’s fewer places for water to escape
(5) waxy, waterproof cuticles on leaves and stems to reduce evaporation